Toxic substances in wastewaters that are released into the aquatic env
ironment cause reduction of phytoplankton uptake up to 50 km away from
the sources depending on the geometry of the coastal sea and the inte
nsity of existing sources. This conclusion follows from an unusual app
lication of the advection-diffusion-interaction equation to the transp
ort of unknown toxic substances. The consequence is that if existing e
utrophication models (without a toxicity submodel) reproduce phytoplan
kton densities in the coastal sea, then probably they have been miscal
ibrated. The problem could be solved by coupling transport of toxic su
bstances to an eutrophication model given that results of uptake exper
iments are available. (C) 1997 Elsevier Science B.V.